12ц1/4-(7ц1/3+1ц1/6)
12ц1/4-(7ц1/3+1ц1/6) = 12ц1/4-(7ц2/6+1ц1/6) = 12ц1/4-8ц3/6 = 12ц1/4-8ц1/2 = 12ц1/4-8ц2/4 = 4ц2/4 = 4ц1/2